Sky's Up Summer 2016 - Page 40

Quadrant 47: — Images and text provided by Howard Eskildsen Craters create chaotic scene The first thing that enters my mind when I view this part of the moon is: What a mess! Rocky rubble litters both sides of the image with a strange array of craters intermixed. In between the rubble, dark lava plains course from top to bottom of the central image, all pocked and marked by craters and rays. The craters themselves seem chaotically varied in size, form and degree of disarray. How can any sense be made of it all? Starting with the craters, it is apparent that some are quite old, while others are fresh and new. The most noticeable young craters are 24 km-diameter Lalande, just to the right of center, and 26 km-diameter Mösting at the upper right. They are the largest youthful craters on the image and show very little wear. Their rims are well defined, and rays radiate from them across lava and rubble in all directions — Lalande’s rays being the brightest. Only a few other smaller craters have rays of any sort and all are quite small in comparison. Mösting A, for example is only 13 km in diameter, and the rest of the rayed craters are much smaller. In contrast, the larger craters on the image show various degrees of wear. Schröter and Sömmering in the upper right image have fragmented rims and filled floors as do Bonpland, Parry and Guericke on the lower left of the image. Additionally, the rims of Ptolemaeus and Alphonsus are worn and scarred by gouges known as Imbrium sculpture. The crater Flammarion has nearly been obliterated. Other craters such as Gambart, Tolansky and Davy formed after the Imbrium event and have intact rims, but were nearly filled by mare basalt lavas that also partly buried some of the rocky rubble and “embay” the margins of the rubble. Another unusual, but not unique feature, is the Davy Crater Chain in the lower right corner of the image. Lunar tidal forces broke up the incoming object that created the chain into a series of smaller fragments. 40 The fragments spread apart slightly and then machine-gunned themselves onto the surface in a series of craters. So the story of the area starts with a now-buried surface in which massive impacts created the large craters, such as Ptolemaeus, Flammarion, Bonpland and others. Sometime later, a supermassive impact to the north of this image created Mare Imbrium and sent mountains of debris flying across the landscape. It buried or scarred everything in its path leaving the debris fields on both sides of the images and creating the deep gouges known as Imbrium sculpture. The cataclysm took only minutes to wreak its devastation across the surface of the moon. Lava flows emerged over long periods of time through cracks created by the massive impact and eventually flooded any low lying areas, filling craters that existed both before and after the massive Imbrium event. Other objects then cratered the solidified basalt, but their rays were since erased by space weathering over Sky’s Up eons. Finally the youngest craters appeared from later impacts, and their rays are still splattered like graffiti across the landscape. As a final insult, the Davy chain Sky’s Up pocked across the moonscape like a drive-by shooting, and the area now appears quite chaotic, but for some very good reasons. 41